2x+4y=12
y=x-3
Since we know what y equals, we can plug this into the first equation:
2x+4(x-3)=12
We can then distribute:
2x+4x-12=12
And solve for x:
6x-12=12
6x=24
x=4
We can then plug x into the second equation and find y:
y=x-3
y=4-3
y=1
Therefore x=4 and y=1